1. Field of the Invention
The present invention relates in general to a method and apparatus for the lubrication of movable pin connections. More particularly, the invention relates to a method and apparatus for the lubrication of pivotable pins used to interconnect the structural elements of floating marine structures.
2. Description of the Related Art
Provision of suitable deepwater floating production platforms for the offshore oil industry is necessary in order to permit economical development of petroleum reserves in the increasingly deep waters in which fields are being located. Economic constraints require that the production platform of efficient design be installed complete on location for costs that are sufficiently low so that maximum profit can be realized. The current designs have their structural assembly substantially completed while in a shipyard, with rigid welded connections being used for interconnecting their primary structural elements. The large size of these current designs requires high lifts by cranes during construction and deep draft channels for towout. Additionally, several of the current designs also require use of a large derrick barge to finish construction offshore. These constraints have very strong negative economic consequences. While adequate in most respects, the current designs are sufficiently expensive that many fields cannot be developed with a sufficiently large positive cash flow to justify the investment risk.
An improved floating platform which has its main structural elements interconnected by movable pin connections is described in copending U.S. patent application Ser. No. 1/344,727 entitled “Selectably Operable Field Mateable Pin Assembly,” filed Feb. 1, 2006, and copending U.S. patent application Ser. No. 11/051,691 entitled “Inclined Leg Floating Production Platform with a Damper Plate”, filed Feb. 4, 2005. This new type of platform does not require high lifts during construction, deep channels for towout, or the use of a large derrick barge for completion of construction offshore. The relatively inexpensive construction and field installation of floating platforms based on the apparatus and methods disclosed in these patent applications are enabled by the use of the movable pin connections described therein.
Pin connections in marine structures have been utilized before for structures such as jackup rigs and for the coupling together of barge-like structures. Additionally, pins have been used in buoyant towers that have large pins at their bases to permit swiveling under environmental and mooring loads. Typically, the pin connections in current use are smaller than the pin connections needed for the floating platform. In addition, pins used in marine structures have generally been located above the sea surface where they can be serviced.
The large size and high transverse loadings of the pins needed for the floating platform necessitate reducing the friction associated with either or both rotational and axial pin movement. Movable pin connections, such as designed for the floating platform having very high loads, require a means of permanent lubrication if the pins are to be maintained in an operating condition over a sustained period. This is particularly the case for the pin connections of the cited copending patent applications, since those connections are immobile for extended periods of up to several years. Additionally for any marine pin connections, corrosion is a serious potential problem, particularly in crevices and gaps between operating components.
A need exists for a lubrication system for marine pin connections that provides lubrication for easing the axial insertion into and retraction from receiving sockets of selectably extendable and retractable pins.
A need also exists for a lubrication system for marine pin connections that provides lubrication for easing rotation of the pins or about the pins.
A further need exists for a lubrication system that will permit isolating marine pin connections from the corrosive contact of seawater.
An additional need exists for a lubrication system that permits the injection of lubricant into a marine pin connection so that galling and fretting of the faying surfaces of the pin connection will be prevented.